Max-Planck-Institut für Dynamik und Selbstorganisation, D-37073 Göttingen, Germany.
J Chem Phys. 2011 Nov 21;135(19):194303. doi: 10.1063/1.3660349.
The role of triplet states in the UV photodissociation of N(2)O is investigated by means of quantum mechanical wave packet calculations. Global potential energy surfaces are calculated for the lowest two (3)A' and the lowest two (3)A'' states at the multi-reference configuration interaction level of electronic structure theory using the augmented valence quadruple zeta atomic basis set. Because of extremely small transition dipole moments with the ground electronic state, excitation of the triplet states has only a marginal effect on the far red tail of the absorption cross section. The calculations do not show any hint of an increased absorption around 280 nm as claimed by early experimental studies. The peak observed in several electron energy loss spectra at 5.4 eV is unambiguously attributed to the lowest triplet state 1(3)A'. Excitation of the 2(1)A' state and subsequent transition to the repulsive branch of the 2(3)A'' state at intermediate NN-O separations, promoted by spin-orbit coupling, is identified as the main pathway to the N(2)((1)Σ(g)(+))+O((3)P) triplet channel. The yield, determined in two-state wave packet calculations employing calculated spin-orbit matrix elements, is 0.002 as compared to 0.005 ± 0.002 measured by Nishida et al. [J. Phys. Chem. A 108, 2451 (2004)].
三重态在 N(2)O 的紫外光解中的作用通过量子力学波包计算进行了研究。使用扩充价四重zeta 原子基组，在多参考组态相互作用水平的电子结构理论上计算了最低的两个 (3)A' 和最低的两个 (3)A'' 态的全局势能面。由于与基态电子态的极小跃迁偶极矩，三重态的激发对吸收截面的远红外尾部只有微小的影响。计算结果没有显示出早期实验研究声称的在 280nm 左右吸收增加的任何迹象。在几个电子能量损失谱中在 5.4eV 处观察到的峰明确归因于最低三重态 1(3)A'。通过自旋轨道耦合促进的 2(1)A'态的激发以及随后向中间 NN-O 分离的排斥分支的 2(3)A''态的跃迁被确定为通向 N(2)((1)Σ(g)(+))+O((3)P)三重态通道的主要途径。在采用计算的自旋轨道矩阵元的两态波包计算中确定的产率为 0.002，而 Nishida 等人测量的产率为 0.005 ± 0.002 [J. Phys. Chem. A 108, 2451 (2004)]。
